1. Field of the Invention
This invention relates, generally, to hand held stereoscopic viewers of the lorgnette type, and more specifically relates to such a viewer having accessory parts that enhance its performance.
2. Description of the Prior Art
Lorgnette stereo viewers are planar in configuration, hand held devices for viewing sterograms or stereographs. Typically, the handle takes the form of a handle member integral with the base plate which carries the lenses of the viewer.
A stereogram or a sterograph is formed by properly positioning two drawings or photographs of the same scene in a certain relation to one another; when properly positioned relative to one another, they form a "stereo pair."
Specifically, the same scene is photographed (as in a stereograph) or drawn or otherwise printed (as in a stereogram) from slightly different angles. Thus, the two views of the scene are homologous because they depict the same scene but are nevertheless different since the common scene is viewed at different angles. The two views are positioned side by side in a common plane, with a small space therebetween, to form the stereogram or stereograph.
Stereograms or stereographs (hereinafter referred to as stereograms for simplicity) must be viewed with a stereoscopic viewing device if the illusion of depth is to be provided to the viewer.
Stereoscopic viewing devices or stereoscopes are of course well known.
The stereoscope shown in U.S. Pat. No. to Petri, 2,849,917, awarded in 1958, is believed to represent the state of the art prior to the filing of the present disclosure.
Petri's device is of the lorgnette style. It has a number of features which advanced the state of the stereoscope art in 1958, but it includes a number of features which limit its utility.
For example, a viewer using the Petri device must have very stable hands. Most individual's hands tremble to some extent when trying to hold an object still, and the trembling usually increases when one is conscious of the fact that trembling is to be avoided, as when a stereogram is to be viewed.
Moreover, when viewing a stereogram, one must square the stereoscope and the stereogram, i.e., the stereogram and the stereoscope must be held in parallel planes.
The Petri device includes no means for stabilizing it, nor does it include any means that would assist the viewer in squaring the stereoscope with the stereogram.
In stereoscopes, a means must be provided to prevent the viewer's left eye from viewing the right member of the stereo pair, and vice versa. Devices which prevent an eye from seeing an image not intended to be viewed by it are called septums.
The septum commonly employed in the earliest stereoscopes was simply an opaque barrier wall that extended from the mid-point of the stereoscope base member to the stereogram or view card, said wall being positioned between the stereo pair of the stereogram and the lens members of the stereoscope.
Later stereoscopes, including Petri's, eliminated the barrier wall and provided the septum by frosting or otherwise rendering opaque the inner (nasal) edges of the lenses.
This technique prevents viewers with narrow interpupillary distances (I.P.D.s) from using the stereoscope; thus, a stereoscope built for viewers with wide I.P.D.s, such as adults, will have no utility for children.
Typically, a stereoscope will be designed for comfortable use by viewer's with very wide I.P.D.s, so that adults having wide-set eyes can use the same. Those adults having smaller I.P.D.s can still see the image if the view card is held further away from the stereoscope, but this merely aggravates the trembling hand problem.
Thus, there is a need for a stereoscope that will accommodate viewer's having a wide range of I.P.D.s.
It follows that there is need for an improved septum means so that the limitations of the masking septums of the prior art can be overcome.
There is also a need for a stereoscope having means enabling it to be held with a minimum of shaking.
Moreover, there is a need for a stereoscope having means which facilitate squaring the stereoscope and the view card.
Broadly speaking, there is a need for a stereoscope that can be provided with accessory parts so that stabilizing means, for example, can be added thereto if desired.
A stereoscope having all of the desireable features outlined herein does not appear in the prior art.